Non-liquid behavior of coalescing droplets of liquid-like cellular aggregates

The fusion of cellular aggregates, such as droplets composed of thousands of epithelial cells, is often modeled by treating each droplet as a liquid-like collection of interacting particles. We conduct numerical simulations of droplet coalescence using both standard particulate models and vertex models meant to more accurately represent the dynamics and mechanics of dense cellular matter. We find that even in the liquid-like regime, the fusion process of model biological droplets can be very different from that of standard liquid coalescence. These differences appear both at the early stages of coalescence (where "thermal" capillary effects are important) and even more markedly at intermediate and late stages (where the scaling laws describing the overall fusion process are characterized by anomalous exponents). We discuss how the character of the model used leads to these unusual dynamical properties. By comparing both our particulate and cellular simulations with experimental results on cell droplet fusion we highlight ongoing challenges in understanding the physics of these mesoscale biological systems.